A method of analysis of physically nonlinear structures is presented that uses an iteration procedure based on changes in the load vector for a given problem. The speed of convergence to the final solution of the method is increased by introducing a relaxation factor. The method is compared with a second method that is based on a modified stiffness matrix iteration procedure. The superiority of the first method is demonstrated as well as its suitability for an interactive design-analysis environment. A computer program, TRANTOWER, in which the method of analysis is used is described also. Several numerical examples illustrate the efficiency of the method of analysis and the design of general space trusses.